In May that year, a 63-year-old woman from Hiroshima Prefecture on the company's tour died while descending the mountain after reaching the summit.

According to Shigeru Masuyama of the Japanese Society of Mountain Medicine (JSMM), the cause of the man's death was apparently not altitude illness.

Sudden deaths at lower altitudes are usually caused by cardiac disease, but various factors must be taken into account at high altitudes where the air is thin, such as cerebral problems, Masuyama said.

The amount of oxygen at the top of Mount Everest is one-third of that at sea level. Climbers conventionally have taken nearly a month to acclimate to the high altitudes before trekking to the top of the mountain.

However, commercial tours, which often include many middle-aged and older people, tend to make the ascent right away by relying on bottled oxygen, rather than spending time and energy adapting to the harsher environment.

The plan for the party the man was on was to use bottled oxygen and reach the summit within three days of leaving the first camp, which is about 7,000 meters above sea level. It is not clear if this plan contributed to the man's death.

In last year's meeting of the JSMM, some experts expressed skepticism about tour groups' reliance on bottled oxygen.

Commercial climbing tours have grown in popularity around the world, particularly for treks up Mount Everest. In Japan, the tours cost about 6 million yen (about $50,000) and have attracted middle-aged climbers and senior citizens.(IHT/Asahi: May 16,2007)